1. Field of the Invention
The invention relates to unmanned aerial vehicles, and more specifically to hybrid lighter-than-air vehicles for persistent, high altitude maneuvering and station keeping.
2. Description of the Prior Art
The United States federal agencies and commercial organizations are dependent on satellites for providing communications, imagery, sensing, and navigation for domestic, theater and global operations. Conventional GEO-synchronous satellites cannot provide high resolution imagery and high-fidelity sensing. Though higher resolution imagery and sensing is available from medium and low-earth orbit satellites, these orbits require large constellations of satellites to provide timely coverage over any given geographical region due to orbit inclinations and revisit times.
Balloon payloads have become more capable in recent years because the cost, size and weight of electronics and high-end processors have dramatically decreased. Over any geographical region, a low-cost balloon hoisted system can provide full coverage, 24 hours a day. However, free floating balloons have no means of maneuvering; they may have some limited active buoyancy control, but remain subject to prevailing wind and will float downwind. Because of atmospheric winds, numerous balloons must be continuously launched in order to provide the continuous coverage over any geographical area. Due to lack of maneuvering, balloons and payloads are difficult to recover.
Unmanned winged aircraft of various configurations are also being used with some drawbacks, such as the time on station limited by fuel and large and expensive logistical requirements to support the aircraft. High altitudes that protect the aircraft from threats and provide greater payload coverage are also difficult to achieve and maintain because of aerodynamic limits of fixed wing aircraft.
What is needed is a hybrid aircraft combining the efficiencies, operating altitudes, and durability of balloons with the station keeping maneuverability of winged aircraft.